Mini Paceman Engine Issue

That does sound like a faulty boost pressure actuator, especially the whistling and hissing noises. Does the hissing sound get louder as you accelerate? The check engine light and reduced power definitely point to a turbo system issue. To confirm, have you tried checking for any obvious leaks in the intake hoses or around the intercooler? A leak there could also cause similar symptoms. It reminds me of a similar issue I had on an older vehicle, though the symptoms were slightly different at the time.

Thank you for your quick response! I have checked the hoses as best as I could, but I am not very experienced with turbo systems. Where exactly is the intercooler located on the Mini Paceman, and what should I be looking for in terms of leaks? Also, how can I test the actuator valve itself?

Given your description, especially the stalling and hissing, it does sound increasingly like the turbo wastegate actuator. The intercooler is usually located at the front of the car, behind the bumper. Look for oily residue or cracks. However, testing the actuator valve directly requires specialized tools and knowledge. Since you mentioned you are not very familiar with turbos, I strongly recommend consulting a qualified mechanic. They can properly diagnose the issue and replace the faulty component. Continuing to drive with this issue could potentially damage the turbo system further.

Thank you very much for your assessment and helpful suggestions. You were right, it was indeed the electrical bypass valve. I had it replaced at a workshop, and the issues are now resolved. The total cost came to around 250€. The car runs smoothly again!